Cooling circuit for an internal combustion engine

ABSTRACT

A cooling circuit for an internal combustion engine includes a first coolant circuit and a second coolant circuit, the cooling circuit being able to be operated by a distributor so that the internal combustion engine reaches its operating temperature as quickly as possible, and a heat exchanger used to heat the vehicle interior is operational as quickly as possible. The return channel from the second coolant circuit is connectable to either the return channel or the flow channel of the first coolant circuit.

FIELD OF THE INVENTION

The present invention relates to a cooling circuit for an internalcombustion engine.

BACKGROUND INFORMATION

A water-cooled internal combustion engine of a motor vehicle is cooledby a coolant, usually water including various additives, which iscirculated through the engine block and the cylinder head of theinternal combustion engine by a main coolant pump. From the cylinderhead, the coolant reaches a radiator or, alternatively, a heatexchanger. A cooling circuit for an internal combustion engine, whichallows the cooling capacity in different areas of the engine to beadjusted to the actual cooling requirements, is described in PublishedGerman Patent document DE 199 38 614.

A known cooling circuit is first described below in connection with FIG.3, and its disadvantages are explained. FIG. 3 shows a schematicrepresentation of a water-cooled internal combustion engine 1. Internalcombustion engine 1 includes a cylinder head 3 and an engine block 5,both of which are cooled by a water cooling jacket that is notillustrated. Internal combustion engine 1 is cooled by a first coolantcircuit 7, which includes a first flow channel 9, a radiator 11, and afirst return channel 13. Installed in first coolant circuit 7 is athermostat-controlled mixer 15, which, as a function of the temperatureof first flow channel 9, controls a bypass 17, which interconnects firstflow channel 9 and first return channel 13 while circumventing radiator11. The thermostat for controlling the mixer 15 is not illustrated inFIG. 3, since thermostats of this type are adequately known in the art.A main coolant pump 19, which conducts coolant to engine block 5 ofinternal combustion engine 1, is installed in first return channel 13.

The section of first flow channel 9 located between mixer 15 andradiator 11, as well as the section of first return channel 13 locatedbetween radiator 11 and bypass line 17, are represented by dotted linesin FIG. 3 to indicate that mixer 15 has fully opened bypass line 17 andprevents coolant from flowing through radiator 11. Mixer 15 assumes thisposition when the temperature of flow channel 9 is still low, i.e., wheninternal combustion engine 1 is still in the cold start phase.

A heat exchanger 23 is supplied with waste heat from cylinder head 3 asneeded via a second coolant circuit 21. Second coolant circuit 21includes a second flow channel 25, a second return channel 27, and asecond bypass line 29. The output of heat exchanger 23 may be regulatedvia a second mixer 31. This output regulation is known in the art and istherefore not described in further detail.

An auxiliary coolant pump 33 is located in second return channel 27.Auxiliary coolant pump 33 is used, according to the known art, toincrease the volume flowing through the heating circuit and thus toboost the heating capacity, especially at low engine speeds. Athermostat 35, which measures the temperature in second flow channel 25,regulates the flow of cooling water through a wiper fluid heater.

As mentioned above, internal combustion engine 1 is still in the coldstart phase, since first bypass line 17 is fully open and coolant is notyet flowing through radiator 11. The directions of coolant flow in firstflow channel 9, first return channel 13, second flow channel 25, secondreturn channel 27, first bypass line 17, and second bypass line 29 areillustrated by arrows in FIG. 3. This representation shows that heat isexchanged between engine block 5 and cylinder head 3 within the internalcombustion engine, due to the thermosiphon effect. As a result of thisinternal heat exchange, engine block 5 reaches its operating temperatureonly at a slow rate, which is undesirable.

SUMMARY OF THE INVENTION

The present invention provides a cooling circuit for an internalcombustion engine that enables the internal combustion engine to bebrought to operating temperature as quickly as possible after startup,without the danger of local overheating. In addition, the coolingcircuit according to the present invention allows heat to be suppliedvery quickly to the heat exchanger, via which heat is supplied to thevehicle interior. To accomplish this, the return channel from the secondcoolant circuit, which supplies coolant to the heat exchanger, isconnectable to either the return channel or the flow channel of thefirst coolant circuit, which discharges waste heat from the internalcombustion engine via the radiator. Connecting the second return channelof the second coolant circuit to the first flow channel of the firstcoolant circuit, while simultaneously taking the second return channelout of service, produces a small cooling circuit that flows through onlythe cylinder head of the internal combustion engine, thus preventing thecylinder head from overheating and allowing the engine block of theinternal combustion engine to reach its operating temperature as quicklyas possible.

In a first embodiment of the cooling circuit according to the presentinvention, a main coolant pump is provided in the first coolant circuit,and an auxiliary coolant pump is provided in the second coolant circuit,so that, if necessary, the discharge of heat from the internalcombustion engine is adjustable to the necessary requirements.

According to further example embodiment of the present invention, abypass line for circumventing the radiator is provided in the firstcoolant circuit, it being advantageous to open or close the bypass linein a temperature-controlled manner so that the temperature of theinternal combustion engine may be maintained at a constant level largelyindependent of the ambient conditions and the internal load of theinternal combustion engine.

To ensure more comfortable heating of the vehicle interior, theauxiliary coolant pump may be regulated or controlled in atemperature-controlled manner.

Optimum performance of the cooling circuit may be achieved by operatingthe cooling circuit according to the following procedure:

-   -   Detection of the temperature of the internal combustion engine.    -   Deactivation of the main coolant pump and the auxiliary coolant        pump; setting of the distributor to its first position if the        temperature of the internal combustion engine is less than a        first threshold value.    -   Deactivation of the main coolant pump and activation of the        auxiliary coolant pump; setting of the distributor to its first        position if the temperature of the internal combustion engine is        greater than or equal to the first threshold value and less than        a second threshold value.    -   Activation of the main coolant pump and deactivation of the        auxiliary coolant pump; setting of the distributor to its second        position if the temperature of the internal combustion engine is        greater than or equal to the second threshold value.

Operating the cooling circuit of the present invention according to theabove procedure ensures that the internal combustion engine reaches itsoperating temperature as quickly as possible, the heat exchanger issupplied with heat as soon as possible and, upon reaching the operatingtemperature, the internal combustion engine is adequately cooled toavoid overheating in all operating states.

To prevent local overheating during the cold start phase of the internalcombustion engine, one may activate the main coolant pump, deactivatethe auxiliary coolant pump and set the distributor to its secondposition if the power output of the internal combustion engine exceeds apreset limit value. The power output of the internal combustion enginemay be calculated, for example, on the basis of the product of therotational speed of the internal combustion engine and the torque outputby the internal combustion engine. Alternatively, either the torque orthe rotational speed alone may be used as the criterion for activatingthe main coolant pump.

As a further security measure, the main coolant pump is activated, atthe latest, upon reaching a maximum pump deactivation time, which may bedetermined as a function of the engine temperature when starting theinternal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary embodiment of a cooling circuit according tothe present invention in a first operating state.

FIG. 2 shows an exemplary embodiment of a cooling circuit according tothe present invention in a second operating state.

FIG. 3 shows a prior art cooling circuit.

FIG. 4 shows a flow chart of a method for the optimum operation of thecooling circuit according to the present invention.

DETAILED DESCRIPTION

FIG. 1 shows an exemplary embodiment of a cooling circuit according tothe present invention in which this undesirable internal heat exchangedoes not take place within internal combustion engine 1. The samecomponents are identified by the same reference numbers as in FIG. 3,and the remarks made in reference to FIG. 3 also apply accordingly toFIG. 1. In addition to the components shown in FIG. 3, the coolingcircuit according to the present invention also includes a distributor39. The position of distributor 39 shown in FIG. 1 establishes ahydraulic connection between second return channel 27 and first flowchannel 9 via first bypass line 17. Main coolant pump 19 is deactivated,preventing coolant from flowing through radiator 11. In this position,the coolant flows from second channel 27 to cylinder head 3 via firstbypass line 17 and first flow channel 9. The coolant is discharged fromcylinder head 3 into second flow channel 25, where it reaches secondreturn channel 27 either via heat exchanger 23 or second bypass line 29.In this configuration of the cooling circuit according to the presentinvention, coolant does not flow through the engine block, which allowsthe engine to reach the operating temperature as quickly as possible.

However, cylinder head 3, which heats up faster than engine block 5, isadequately cooled to avoid impermissibly high operating temperatures incylinder head 3. If necessary for thermal reasons, it is possible toalso cool the upper area of the cylinders (not illustrated) in theinternal combustion engine via cylinder head 3, since this area alsobelongs to the combustion chamber and therefore is subjected to rapidheating in the cold start phase. This configuration also ensures thathot coolant flows through heat exchanger 23 as quickly as possible sothat the latter may discharge heat as quickly as possible.

If not only main coolant pump 19, but also auxiliary coolant pump 33, isdeactivated at the beginning of a cold start, cylinder head 3 may reachits operating temperature in just a few seconds or minutes, causing theemissions of internal combustion engine 1 to drop very quickly after thecold start begins. A temperature sensor for measuring the componenttemperature at the internal combustion engine, e.g., in the area ofcylinder head 3, makes it possible to prevent impermissible overheatingof the cylinder head. Once cylinder head 3 has reached an adequatetemperature, auxiliary coolant pump 33 may be activated, and the stateillustrated in FIG. 1 occurs.

FIG. 2 shows the cooling circuit illustrated in FIG. 1, with distributor39 assuming a position connecting second return channel 27 to firstreturn channel 13. In FIG. 2, the directions of coolant flow are alsoindicated by arrows. In this state, main coolant pump 19 is activated sothat engine block 5 is also cooled by coolant. Mixer 15 regulates theoutput of first coolant circuit 7 in the same manner as shown in FIG. 3.The output of heat exchanger 23 is also regulated as shown in FIG. 3.

The cooling circuit according to the present invention enables aninternal combustion engine to reach its operating temperature as quicklyas possible without resulting in disturbing internal heat convection.Different assemblies of internal combustion engine 1 may therefore reachtheir operating temperatures at different rates. For example, cylinderhead 3 usually reaches its operating temperature before engine block 5.As soon as cylinder head 3 has reached an adequate temperature, heat maybe discharged via second coolant circuit 21 and used to heat the vehicleinterior via heat exchanger 23.

FIG. 4 shows a flow chart of a method for operating a cooling circuitaccording to the present invention. Internal combustion engine isstarted in a step S1. Immediately after the internal combustion enginestarts, a maximum pump deactivation time P_(off, max) is set as afunction of the engine temperature. This takes place in step S2. A thirdstep S3 checks whether the main coolant pump (abbreviated as HWP) isdeactivated for longer than maximum pump deactivation time P_(off, max).If this is the case, main coolant pump HWP is activated. A fourth stepS4 checks whether the power supplied to the internal combustion engineexceeds a limit value P_(limit), If this is the case, the main coolantpump is activated to avoid overheating the internal combustion engine.Otherwise, a step 5 checks whether temperature T_(eng) of the internalcombustion engine is less than a first threshold value T_(S1). If thisis the case, main coolant pump HWP as well as the auxiliary coolant pump(abbreviated as ZWP) are deactivated, and distributor 39 is set to itsposition shown in FIG. 1. This procedure takes place in a step S6. Thequery then starts over again at step S3. If temperature T_(eng) of theinternal combustion engine is greater than first threshold value T_(S1),main coolant pump HWP remains deactivated, auxiliary coolant pump 33 isactivated, and distributor 39 is closed. When distributor 39 is closed,this means that it has assumed its position shown in FIG. 1.

These operations take place in step S7. If temperature T_(eng) of theinternal combustion engine is less than a second threshold value T_(S2)but greater than first threshold value T_(S1), the sequence starts overagain with third step S3. Otherwise, main coolant pump HWP is activated,auxiliary coolant pump ZWP is deactivated, and distributor 39 is opened,i.e., it assumes its position shown in FIG. 2 and connects first returnchannel 13 to second return channel 27.

Operating the cooling circuit of the present invention according to themethod described in FIG. 4 provides maximum protection of the internalcombustion engine against overheating, while simultaneously allowing itto reach its operating temperature as quickly as possible. The vehicleheating system may also be placed into service very quickly.

1-15. (canceled)
 16. A cooling circuit for an internal combustionengine, comprising: a first external coolant circuit including a firstflow channel, a first return channel, and a main coolant pump, whereinthe first external coolant circuit supplies waste heat from the internalcombustion engine to a radiator, and wherein the first flow channel isconnected to the cylinder head of the internal combustion engine; asecond external coolant circuit including a second flow channel, asecond return channel, and an auxiliary coolant pump, wherein the secondexternal coolant circuit supplies waste heat from the internalcombustion engine to a heat exchanger, and wherein the second flowchannel is connected to a cylinder head of the internal combustionengine; and a distributor having a first position and a second position,wherein in the first position the distributor connects the first returnchannel to the second return channel, and wherein in the second positionthe distributor connects the second return channel to the first flowchannel and the auxiliary coolant pump delivers coolant from the secondreturn channel to the first flow channel, thereby bypassing an engineblock of the internal combustion engine.
 17. The cooling circuit asrecited in claim 16, further comprising a bypass line provided in thefirst coolant circuit to bypass the radiator.
 18. The cooling circuit asrecited in claim 17, wherein the bypass line is selectively opened andclosed depending on temperature.
 19. The cooling circuit as recited inclaim 17, wherein the distributor in the second position connects thesecond return channel to the first bypass line.
 20. The cooling circuitas recited in claim 18, wherein the auxiliary coolant pump is controlledas a function of temperature.
 21. A method for controlling a coolingcircuit for an internal combustion engine, comprising: detecting atemperature of the internal combustion engine; deactivating a maincoolant pump and an auxiliary coolant pump, and setting a distributor toa first position, when the temperature of the internal combustion engineis less than a first threshold value; deactivating the main coolant pumpand activating the auxiliary coolant pump, and setting the distributorto the first position, when the temperature of the internal combustionengine is at least equal to the first threshold value and less than asecond threshold value; and activating the main coolant pump anddeactivating the auxiliary coolant pump, and setting the distributor toa second position, when the temperature of the internal combustionengine is at least equal to the second threshold value.
 22. The methodas recited in claim 21, wherein the main coolant pump is activated, theauxiliary coolant pump is deactivated, and the distributor is set to thefirst position, when a power output of the internal combustion engineexceeds a threshold limit value.
 23. The method as recited in claim 22,wherein the power output of the internal combustion engine is calculatedaccording to the following formula:Power output=M _(eng) ×n _(eng), wherein M_(eng) is the torque output bythe internal combustion engine, and n_(eng) is the rotational speed ofthe internal combustion engine
 24. The method as recited in claim 21,wherein the main coolant pump is activated, the auxiliary coolant pumpis deactivated, and the distributor is set to the first position, whenone of a torque output of the internal combustion engine and arotational speed of the internal combustion engine exceeds a thresholdlimit value.
 25. The method as recited in claim 21, wherein the maincoolant pump is activated, at the latest, after a predetermined maximumdeactivation time has been exceeded.
 26. The method as recited in claim25, wherein the predetermined maximum deactivation time is dependent ona coolant temperature at the time the engine is started.
 27. The methodas recited in claim 21, wherein the auxiliary coolant pump is alsoactivated as a function of the temperature in the second flow channel.28. The method as recited in one of claim 21, wherein the auxiliarycoolant pump is also activated as a function of a component temperatureof the internal combustion engine.
 29. The method as recited in claim28, wherein the component temperature of the internal combustion engineis a temperature inside a cylinder head of the internal combustionengine.